Crystallization phenomena in polymers - Effect of melt conditions and the temperature of crystallization on the course of the crystallization in polyethylene terephthalate

A detailed analysis has been made of the course of crystallization in polyethylene terephthalate at different temperatures and from different preceding melt temperatures. The theoretical deductions based on the mechanisms surmised in part II and kinetical analysis of the density changes with time have been confirmed by direct microscopic examination of the resulting structures. The crystallization constant K in the expression e=c-Ktn, which can be obtained from the analysis of the density-time curves, contains nucleation and growth constants. Measurement of these, on microtomed sections of polymer crystallized for various lengths of time, enables the value of K to be calculated by an independent method. Good agreement is obtained between the values of K ascertained by both methods. The value of n can be 2, 3 or 4 in the case of polyethylene terephthalate, depending on the nucleation and growth processes involved. These vary with the temperature of the crystallization, and the transition temperatures at which n changes in value can be varied by adjusting the previous melt history of the polymer. The direction in which these transition temperatures can be varied by adjusting the melt conditions accords with the theory given in part II.